In conventional liquid-fuel burners, liquid fuel atomization is effected by means of a single liquid-fuel jet or multiple liquid-fuel jets surrounded by a high velocity atomizing stream that is usually air, steam, oxygen or other gases used in the burner. The atomizing medium travels at velocities greater than approximately 100 meters per second for "air-blast atomizers" and up to sonic velocity for "air-assist atomizers", to cause the liquid-fuel to break up into small droplets suitable for combustion. For air-assist atomizers, the supply pressure of the atomizing medium, the angle of impact between the liquid jet and the flow rate of high velocity atomizing medium stream determines the mean drop size distribution. However, the use of high pressure oxygen as an atomizing medium, instead of an air stream or other atomizing gases in oxygen-fuel fired burners leads to a chain of operational problems. First, the expansion of high pressure atomizing oxygen at the burner tip results in a high oxygen velocity, which thoroughly mixes with liquid fuel during the atomization process. The liquid fuel-oxygen mixture thus formed is readily combustible in a high temperature environment. The absence of inert nitrogen and highly reactive oxygen promotes rapid and uncontrolled combustion resulting in a very high temperature flame in the vicinity of the oxy-fuel burner tips which generally leads to the following conditions:
1. Deterioration/oxidation of burner nozzles. PA1 2. Damage to burner block refractory material, which sometimes melts and obstructs the normal flame direction inside the burner block cavity. PA1 3. Undesirable heating of furnace sidewalls, which is also a heat loss to the surroundings. PA1 4. Short flame, due to smaller droplet-size distribution and higher reaction rates, coupled with non-uniform heat distribution to the furnace load. PA1 5. Increased volatilization of certain batch ingredients, e.g. in the manufacture of glass PbO, Boron-containing species, etc. PA1 6. Decreased productivity in pure product quality. PA1 7. Shorter burner nozzle life and increased maintenance.
The economics of the process are also affected by the type of atomization used. In general, a high pressure liquid oxygen supply is relatively more expensive than a low-pressure gaseous oxygen produced by pressure or vacuum swing (PSA or VSA) adsorption units at the site. The use of high-pressure atomizing oxygen requires either a separate liquid oxygen storage and high-pressure supply system or a special oxygen compressor, to boost a low-pressure gaseous oxygen produced in PSV/VSA type units to high pressure required for atomization. Either scheme adds to the cost of utilizing oxygen in a liquid-fuel burner, thus increasing production costs for the user.
Furthermore, it has been observed that the use of high pressure oxygen for atomization (greater than 10 psig) leads to a very noisy and intense oxy-fuel flame, which has limited latitude, as far as flame shape or length control is concerned. The flame momentum is extremely high, due to high combustion velocities, which may result in overheating of burner tips, burner block, and furnace refractory.